7 definitions
by
Count Vlad of Mongosteinergarten

The apotheosis of bullet weaponry, the boltgun is a perfectly-crafted firearm gifted only to the Emperor's finest. Boltguns fire shells which explode shortly after penetration, inflicting massive tissue damage.

The Urban Dictionary T-Shirt

The more common term for boltgun.
Note that heavy assault troops tend to make use of a double-barelled version known as a storm bolter, and support troops and vehicles extensively utilise heavy rapid-fire versions known as heavy bolters.